Such alumina base ceramics have been used as a cutting tool or a wear resistant member for high-speed machining and hot working where a conventional tool material such as a tool steel, a high-speed steel, a cemented carbide or the like is difficult to use, because of its comparable easiness for producing a compact sintered body among conventional ceramic materials.
However, the alumina base ceramics is disadvantaously limited in use because of their poor strength and toughness.
Sintered Al.sub.2 O.sub.3 dispersion-strengthened with carbide or carbo-nitride particles such as TiC or Ti (C,N) in order to improve the properties, so-called black ceramics have been developed. However, such black ceramics is lack in reliability when applied for machining under a heavy load such as rough cutting of steel or cast iron, because of its insufficient strength and toughness.
Further, since a sintered Al.sub.2 O.sub.3 added with WC particles is improved significantly in strength and toughness, and has a high hardness, it has been tried to apply to wear resistant members.
For example, Japanese Patent Laid-Open No. 3-290355 discloses that a high hardness and high toughness sintered body having a density of more than 90% of the theoretical can be provided by subjecting a starting powder consisting of Al.sub.2 O.sub.3 added with 10-90% by volume of WC to normal sinterinig, hot pressing, or hot isostatic pressing.
It is also disclosed in Japanese Patent Laid-Open No. 5-279121 that a sintered body obtained by adding 5-95 wt % of WC to Al.sub.2 O.sub.3 followed by sintering at 1400-1950.degree. C., and making W.sub.2 C phase appear due to existence of oxygen of 0.05-6 wt. % in the WC starting powder is excellent in strength and toughness.
However, these Al.sub.2 O.sub.3 -WC ceramics can not exhibit sufficient wear resistance under a severe condition of high-speed cutting of steel or cast iron, since the oxidation resistance at high temperature is insufficient although it is surely excellent in strength and toughness. Therefore, these ceramics are hardly used for a member requiring high-temperature wear resistance such as cutting tool.